Extract bugreport collection from DPMS

Also moved the content of RemoteBugreportUtil to the new class.

Bug: 164030902
Test: atest DevicePolicyManagerTest#testGetLastBugReportRequestTime
Test: atest DeviceOwnerTest#testRemoteBugreportWithTwoUsers
Test: CtsVerifier / Device Owner Requesting Bugreport Tests
Change-Id: Idc06c3ea7400fcd883309135d3d4365aeb1b181b